1. Field of the Invention
The invention relates to a stranded wire composed of a plurality of metal strand wires twisted together. The wires may be joined to one another throughout their entire length or locally, or may be joined together only when the stranded wire is to be used. The wire may be provided with an insulating sheath. In general stranded wire has better flexibility and resistance to repeated bending than a single-wire conductor of the same electrically effective metal diameter.
Connecting a stranded wire by a soldered or crimped connection frequently proves difficult in practice, because the individual strands fan out after the wire has been cut to the required length and the insulating sheath has been removed.
2. Description of the Invention
According to one known practice, an additional operation is required in which the individual strands, which have been bared on removal of the insulating sheath, are again twisted together. This operation is generally followed by the provision of solder metal to the wire ends so as to join them to form a single unit. Such operations involve relatively high labor costs and adversely affect the bending strength of the wire at the location of the soldering. Moreover the amount of solder applied in general is large and undefined; hence when using a crimped connection the electrical contact is likely to be unstable, because the solder will flow under the pressure used for crimping.
Stranded wires are known which are made by twisting together metal strands coated with solder throughout their length. In these wires the solder coating has a thickness such that, when manufacturing stranded wire lengths by cutting a larger length into pieces, the twisted strands can be joined together by local heating. This may be effected, for example, by joining the individual strands to one another by induction heating at the locations at which the insulation is to be removed. Stranded wires used for this purpose have the disadvantage that each individual strand is provided with a comparatively thick solder coating. The provision of a solder of the required thickness and the amount of solder concerned cause the price of such wire to be comparatively high.
Stranded wires are also known in which, during manufacture, individual metal wires are joined together throughout their length by solder. An advantage of such wire is that the solder can be applied after the bare strands have been twisted together so that at least one operation is dispensed with. A disadvantage is that part of the flexibility is lost. Another disadvantage is the comparatively large use of solder and the poor reproducibility of the process. However, the stranded wire still has a considerably higher resistance to repeated bending than a solid conductor of equal diameter.
It is also known to manufacture wire for underwater cables by coating a central wire, by means of an extrusion process, with an insulating mantle consisting of polyethylene or a copolymer thereof which contains a hardener, such as an organic peroxide. The thickness of such an insulating mantle is about 100 .mu.m. A plurality of wires is twisted around the insulated wire and the assembly is provided with an outer sheath of polyethylene or a copolymer thereof which also contains a hardener. Finally the resulting wire is hardened at increased temperature and pressure. During this process the initial interstices between the wires are entirely filled with polyethylene whilst the insulating mantle and the outer sheath are firmly bonded to one another by cross-linking.
A disadvantage of this known method is that the cable obtained is solid and its flexibility is reduced.